A study was made of the effects of fructooligosaccharides, which exist widely inplants such as onion, edible burdock, wheat etc., on the human and animal intestinal flora. Fructooligosaccharides are produced from sucrose with the aid of β-fructofuranosidase from Aspergillus niger on a commercial scale by Meiji Seika Kaisha, Ltd.(Neosugar, Meioligo®). It has been found that they are not hydrolyzed by any digestive enzymes of humans and animals. Moreover utilization byvarious kinds ofintestinal bacteria indicated that Bifidobacterium spp., the Bacteroides fragilis group, Peptostreptococcus spp. and Klebsiella pneumoniae can utilize these saccharides, but Clostridium perfringens, Escherichia coli and others cannot. The fructooligosaccharides are selectively utilized, particularly by bifidobacteria.The clinical studies showed that fructooligosaccharides administration improved the intestinal flora, with subsequent relief of constipation, improved blood lipids in hyperlipidemia, and suppressed the production of intestinal putrefactivesubstances.